A term of Hawaiian origin. Used in reference to a basaltic lava that occurs in flows with a fissured, rough and jagged surface.
A Hawaiian name (pronounced ‘ahah’) for one of the two chief forms of lava emitted from volcanoes of the Hawaiian type, the other being pahoehoe. ‘The second form of the lavas is called by the natives a-a, and its contrast with pahoehoe is about the greatest imaginable. It consists mainly of clinkers sometimes detached, sometimes partially agglutinated together with a bristling array of sharp, jagged, angular fragments of a compact character projecting up through them. The aspect of one of these aa streams is repellent to the last degree, and may without exaggeration be termed horrible. For one who has never seen it, it is difficult to conceive such superlative roughness’ (Dutton, USGS, 1883). One eruption may emit aa in one direction and pahoehoe in another, or both types may occur in the same lava-stream. These two names are applicable to lavas of any geological age, in so far as the physical structure characterizing them can be recognized. The two forms are often referred to as block lava and ropy lava.
No related terms.